1. Field of the Invention
This invention relates to a process for reducing the content of free formaldehyde and formic acid in nonionic and anionic surfactants by addition of selected amine compounds.
2. Discussion of Related Art
Nonionic and anionic surfactants are important raw materials for the production of personal hygiene preparations and cosmetic preparations such as, for example, foam baths, hair shampoos, body lotions or creams. Typical representatives of such surfactants are, for example, ethoxylated partial glycerides, fatty alcohol polyethylene glycol ethers and fatty alcohol ether sulfates.
However, nonionic and anionic surfactants containing ethylene oxide units in the form of polyethylene glycol ether chains are not indefinitely stable to oxidative degradation. Accordingly, in the event of prolonged storage, particularly under the influence of light and oxygen, the polyethylene glycol ether chain can undergo partial degradation with formation of formaldehyde or formic acid. Although both these substances are permitted preservatives for cosmetics and although the quantities formed are usually far below the legal limits, raw material manufacturers strive to produce surfactants with a high degree of purity, i.e. with a minimal content of impurities or degradation products. With this in mind, therefore, there is a continuing interest in minimizing the content of unwanted free formaldehyde and formic acid in anionic and nonionic surfactants.
It is known from a contribution by Donbrow on the stability of polyoxyethylene chains in Surfactant Science Series, Vol. 23, M. J. Schick (ed.), Marcel Dekker, Inc., New York/Basel, 1978, pages 1011 et seq. that the oxidative degradation of such chains is initiated and promoted by various factors and, depending on the mechanism, can be stopped by the addition of antioxidants, peroxide scavengers, chelating agents or UV adsorbers. In this connection, it is pointed out for example that phenols and amines react off with free radicals and can thus prevent the formation of peroxides.
The use of phenols and alkylamines for stabilizing products which come into contact with the human skin in their commercial form is out of the question for toxicological reasons alone. The odor-emission problems involved in their use and difficulties of making up also rule out these substances.
Accordingly, the problem addressed by the present invention was to provide a process for reducing the content of free formaldehyde and formic acid in nonionic and anionic surfactants which would be free from the disadvantages mentioned above.